(a) Field of the Invention
The present invention relates to a method for eliminating interference. More particularly, the present invention relates to a method for eliminating an interference signal in adaptive array systems including an antenna array system and an adaptive sensor array system, and an adaptive array processor using the method.
(b) Description of the Related Art
Generally, an interference signal, a path loss, multipath fading, and a signal delay may be generated by radio propagation channel characteristics in areas relating to radar, sonar, and wireless communication. Particularly, since system performance is deteriorated by distortion caused by the interference signal (i.e., a signal that is not required), methods for eliminating the interference signal are actively being studied.
When a signal required at an output of an array system is estimated, a range of correlation between a required signal (hereinafter referred to as an “original signal”) and the interference signal affects the estimation. When the interference signal does not correlate to the original signal, the interference signal may be fully estimated at the array output without any distortion while protecting the original signal. For this purpose, a linearly constrained adaptive array processor algorithm has been suggested. Here, in a linearly constrained least mean square (LMS) algorithm, an array weight is updated from a direction for estimating the original signal (i.e., an original signal direction) to a unit gain constraint.
However, when the interference signal partially or completely correlates with the original signal, the original signal may be partially or completely eliminated by correlation between the original signal and the interference signal while adaptively processing a signal input to a system. Therefore, it is difficult to estimate the original signal.
To prevent signal cancellation in a coherent signal environment, a hardware or software approach method may be used in an adaptive array system.
The hardware approach method includes a method using a master-slave type of array processor. In the method, two array processors are required, and one of the two is an adaptive processor and the other is a non-adaptive processor. A master processor uses a phase delay element and subtractive preprocessors to eliminate the original signal in an adaptive process.
Accordingly, the array weight along with subtracted interference is repeatedly updated, and therefore the array weight generated in the master processor is not affected by the original signal. Therefore, the obtained array weight is copied into a slave processor, an input signal including the original signal having passed through the phase or time delay element is processed based on the copied array weight, and the array output is generated.
However, in the above conventional method, there is a problem in that an additional array process is required (i.e., two array processors are required) to prevent the signal cancellation. In addition, compared to a method using one array processor, the number of computations required to generate the array output is large. Further, when the phase or time delay element or the subtractive preprocessors used in the master processor are deteriorated, the partial signal cancellation may be generated by leakage of the original signal, and signal estimation performance is reduced.
A spatial smoothing approach method is used to prevent the signal cancellation. In the spatial smoothing approach method, a subarray preprocessor is used, in which input correlation matrices of a subarray are averaged and the input correlation matrices are nearly diagonal so as not to correlate coherent input signals with each other. Accordingly, since the coherent interference is not correlated after the preprocessor, the coherent interference is efficiently eliminated.
However, in the spatial smoothing approach method, as the number of interference signals increases, it is required to increase the number of subarrays to efficiently eliminate the interference, and therefore the larger number of elements is problematically required. Compared to the method using one array processor, the number of computations is increased by the number of used subarrays.
In addition, a method using a parallel spatial processing algorithm is used to prevent the signal cancellation. In the method, to eliminate the coherent interference, the subarrays are processed in parallel, and delayed outputs of the subarrays are averaged to generate the array output.
The number of computations is not larger than that of the spatial smoothing approach method since the input signal is processed in parallel between the subarrays. However, there is a problem in that the number of elements corresponding to the number of subarrays is required to efficiently eliminate the coherent interference.
As described, according to the prior art, the larger number of elements or an additional array processor is required to eliminate the coherent interference, and therefore the hardware is increased and the larger number of computations is problematically required.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention.